When Liu placed fertilised human embryos created during IVF treatment inside, they nestled into the wall of the womb and began to attach themselves to the endometrial cells that make up the lining — just as in the early stages of pregnancy. Liu stopped the experiments after a week because regulations prevent human embryos being developed much further.

No such restrictions apply to animals and, in unpublished work, Liu says she has now grown mouse foetuses in her artificial womb for 17 of their 21—day terms. This is equivalent to about 31 weeks in humans, at which point babies have been viable for more than a month and can routinely be nurtured to normal development if born prematurely.

Just as with the human embryos, the tiny bundles of mouse cells nestled into the artificial womb lining and began to attach themselves. Liu watched as blood vessels formed, then miniature placentas and, eventually, the amniotic sac — an embryo's personal protective bubble.

A different approach has been taken by Yoshinori Kuwabara at Juntendo University in Tokyo. His team has removed foetuses from goats and placed them in clear plastic tanks filled with amniotic fluid stabilised at body temperature. In this way, Kuwabara has kept goat foetuses alive and growing for up to 10 days by connecting their umbilical cords to machines that pump in nutrients and dispose of waste.

While Liu's work is aimed at helping those having difficulty conceiving, Kuwabara's is designed to help women who suffer miscarriages or very premature births. In this way Liu is extending the time an embryo can exist in a laboratory before being placed in a woman's body; Kuwabara is trying to give a foetus a safe home if expelled too early from its natural womb.

Crucially, both believe artificial wombs capable of sustaining a child for nine months will become reality in a few years.

This Slate article looks at artificial wombs as a way of incubating embryonic tissue for use in regenerative medicine, not as a way to create a new person. There must be many uses for working artificial wombs, if you think about it.

Ethicists have lined up on every conceivable side of the issue. Some feminists see the development as an emancipation of women, and some see it as a threat to the existence of all women. Choose your sides. Some religious fundamentalists see artificial wombs as the end of abortion, and some see them as a threat to the idea of "human essence." Like a rorschach blot test, the artificial womb concept has a way of causing people to define themselves in unexpected ways.

Embryos have implanted inside the abdominal cavities of women, on the outer surface of viscera, and developed to a surprising degree. Here is a report of a successful abdominal pregnancy and delivery. This suggests that an artificial womb constructed of living tissue, well perfused with nutrient and oxygenating fluid, should do just as well as this woman's abdominal organs, and create much less risk for the mother. The problem of providing an in utero like environment should be solvable.

It will happen, sooner or later, ethics or no ethics, laws or no laws. What we choose to make of the possibilities created by the artificial womb is up to us.

Far into the future, I foresee an artificial womb in every home, where the proud parents-to-be can keep close track of thousands of parameters in the developing fetus. The A.W. could even be fitted with a 2-way communications (cell phone with remote antenna for radiation safety) device and high fidelity speakers so that the fetus can listen to Mozart, a soothing heartbeat, or even the mother's voice from half a world away, if need be.